Hitler was determined to go to war and work towards world domination. I feel most certain that there was nothing the rest of the world could have done to prevent this from happening.
It would have been easier in Europe than in Asia to prevent World War II, in my opinion. Hitler's Germany was not very strong as late as 1937. If France, which had a 5 million member military, had challenged him directly as soon as he reoocupied the Rhineland, or annexed Austria, they might have unseated Hitler before the war ever got started in earnest.
In discussing what more, if anything, could have been done to prevent World War 11, it is interesting to remember the catchphrase "Jaw-Jaw, Not War-War." Although I believe very strongly in this talking idea, it only works with rational thinking people - not those who are crazy either with power or through a psychological illness or borderline personality disorder. The points about the low self-esteem of the German are very true, but in hindsight we have to wonder if they rallied their dissent to the wrong flagpole - Hitler was probably mentally ill, but it took the world too long to realize and act on his sick madness - a little like MacBeth?
This is a fairly powerful question. The previous post identified the strong point of making the Versailles treaty less harsh. If the assumption can be made that individuals of the time period could do so, I would say that they needed to exercise more of a voice of dissent to the rise of the dictator in Europe at the time. While there were some active voices in support of these leaders at the start of their emergence to power, many others were simply politically apathetic and dismissive of the political realities that were to emerge. Europeans, so shattered with the losses of the First World War, were of the mindset to not be able to feel comfort enough to voicing their own dissent to what many of them knew was wrong. In the end, their apathy or silence, along with the world's, helped to allow leaders like Mussolini, Hitler, and Stalin to rise to power and help move the world into World War II.
Had the leaders of the Allied countries not been in such a hurry to punish the Germans, there would have been a possibility of avoiding WWII. Forcing the Germans to accept responsibility for the war, humiliating them, stripping them of their colonies and thereby resources, led Germans to feel bitter about the Treaty of Versailles.
On the other hand, as the US and Western Europe all suffered through a deep economic depression during the 1930s, the Germans may have attempted to gain more territory/resources anyway.
I think that the only thing that could possibly have been done to prevent WWII would have been to make the Treaty of Versailles less harsh. That would, I think, have made the Germans less bitter towards the rest of the world and it might have made them have a lot less in the way of economic problems.
If the Germans had been less angry and their economy had been better off, they would have been less likely to go for an angry person like Hitler for their leader.
If the war in Europe hadn't started, the war in the Pacific would have been much less likely as well.
We can think of so many theoretical possible ways of preventing wars in the world. League on nation formed after World War I, represented the best solution that the the world as a whole could find to prevent major wars in the world. This initiate failed clearly and miserably with the happening of World War II. After World War II, many nations of the world created United Nations Organization to promote lasting peace in the world and to prevent war. Perhaps this body is more powerful and active then the League of Nations, the net results are still far from satisfactory.
In conclusion, it appears that joint initiatives by multiple countries can help significantly in promoting peace and harmony. But the day when the world can totally prevent any war from happening appears to be far off.